swift234

IRGen: Optimize copy/destroy of ObjC tagged or nullable enums too.

Rename TypeInfo::isSingleRetainablePointer to TypeInfo::isSingleSwiftRetainablePointer, and add an isSingleUnknownRetainablePointer entry point to ask whether a type has any single-refcounted representation, native or not. Use that to provide the same nullable-pointer and pointer-with-tag optimizations for copying and destroying enums with ObjC payloads as we do for Swift class payloads.

Swift SVN r12410